1. Field of the Invention
The present invention relates to an interface for a receiver, in particular for use with a conditional access sub-system, and a method of arranging such an interface.
2. Description of the Related Art
Set top boxes are known for digital video broadcasting (DVB). These decode a received digital video broadcast and provide suitable signals to a television, such that the received images may be displayed. Broadcasts often comprise scrambled or encrypted signals, such that only an authorised receiver can watch the broadcast television programs. In this respect, the set top box includes a conditional access system which is able to descramble a transmitted broadcast.
It has been proposed to provide a generic DVB receiver which could be provided as a set top box or as part of a television itself. To enable the DVB receiver to be used with various broadcast services, it has also been proposed that the DVB receiver should be provided with a number of sockets, each able to receive a conditional access sub-system (CASS) module. In particular, a standard has been proposed in the publication xe2x80x9cCommon Interface Specification for Conditional Access and Other Digital Video Broadcasting Decoder Applications CENELECEN50221xe2x80x9d. Each CASS module can hold information for descrambling one or more transmitted broadcasts. It can also hold service entitlement information, be controlled by the service provider and the service provider can communicate with the CASS module using encrypted messages carrying descrambler keys as service management information.
An interface is therefore to be provided between the common digital TV receiver and the CASS module sockets to allow each service provider to use their own unique conditional access system and allow the user to change the conditional access systems without changing the receiver.
The interface should allow a user to connect less than the maximum number of CASS modules to the receiver interface in arbitrary positions without hindering the correct functioning of the device.
According to the present invention, there is provided a method of arranging an interface for connecting one or more conditional access modules to a receiver, the interface including a plurality of interface sections, each for connection with a respective socket for receiving a conditional access module and each having a plurality of input lines and a plurality of respective output lines for connection to said socket, the method comprising:
arranging the interface sections in series, with the input lines of one interface section connected to the respective output lines of the next interface section, and
connecting the output lines of each interface section to the input lines of the same interface section via an electronically controllable switch, such that, when a conditional access module is not connected to the socket of an interface section, that socket may be selectively by passed.
There is also provided an interface for connecting one or more conditional access modules to a receiver, the interface including:
a plurality of interface sections, each for connection with a respective socket for receiving a conditional access module and each having a plurality of input lines and a plurality of respective output lines for connection to said socket, the interface sections being arranged in series, with the input lines of one interface section being connected to the respective output lines of the next interface section and with each interface section including an electronically controllable switch connecting the output lines of that interface section to the input lines of the same interface section, such that each socket may be selectively by passed.
In this way, an apparatus in which the interface is used may control the interface to by-pass sockets where conditional access modules have not been connected. In particular, where, for instance, three out of four sockets are used, the apparatus can determine that the fourth socket is not in use and, therefore, by-pass it. In this way, a data transport stream may be passed consecutively between each interface section, socket and conditional access module without interruption.
It is proposed to provide 11 input and output lines, as will be discussed below. However, conventional switching circuits use 8 way switches. In order to carry out the necessary switching for the present invention, two parallel 8 way switches would be required, creating, not only undue cost in additional components, but also redundancy in the circuit itself.
Therefore, according to a preferred feature, the present invention uses 11-way tristate buffers for the electronically controllable switches.
When a conditional access module is connected to a socket, it may be necessary for it to go through an initialization process driven by other lines and pins not considered here. With the conditional access module connected to the series arrangement interface, problems may arise as a result of transport stream data passing to the CASS modules.
Therefore, according to a preferred embodiment, it is proposed that each interface section includes an electronically controllable output gate for connecting the plurality of output lines of that interface section to a respective socket, the output gate being controllable by a control line to be selectively driven to a predetermined level irrespective of the levels of the output lines.
Preferably, the predetermined level is zero.
While the above described arrangement is highly advantageous in function, it may be unsatisfactory in complexity and cost, requiring multiple connections and possibly the production of dedicated 11 way components.
In view of this, according to a preferred embodiment, each interface section may be part of a transport stream handler which is additionally controllable to selectively connect the plurality of output lines of that interface section to the respective socket or output a predetermined level in place of the levels on said plurality of output lines.
Hence, according to the present invention there is also provided an integrated circuit for use in a receiver, the integrated circuit comprising 11 input lines, 11 first output lines connected to the respective 11 input lines, 11 second output lines, an enable line for selectively connecting the input lines to the respective second output lines and a control line for selectively driving all the first output lines to zero irrespective of the levels of the input lines.
In this way, an interface section is produced generally as a single component, such that both the function of by-passing a socket and selectively driving the output lines to a zero level can be implemented with the same device. The overall pin count for the interface may be reduced, since the input to both the by-pass switch and the logic gate are common, thereby reducing construction costs. Furthermore, only a single dedicated circuit need be produced, thereby making it more economically viable.
The present invention also has the advantage of very readily allowing the scaling of a device. In particular, a device using two interface sections or sockets can easily have further interface sections or sockets inserted with no other redesign requirements.
Preferably, the receiver is a digital video receiver, such as a DVB receiver.
Preferably, the sockets used are standard PC Card sockets, for instance as defined by the PCMCIA (Personal Computer Memory Card Industry Association) in the PC Card standard, February 1995.